<?php

$captcha = array(
    'length' => 5,
    'width' => 300,
    'height' => 100,
    'bg_color' => array(238,239,239),
    'br_color' => array(208,208,208),
    'session' => 'm_app_session_name_for_captcha'
);

$config['captcha'] =& $captcha;